A generic method is known from DE 103 59 071 B3, in which method, in order to briefly increase the driving power of a drive unit, composed of an internal combustion engine and an electric machine, of a hybrid vehicle, the electric machine is at least temporarily connected to the internal combustion engine for a boosting mode. The electric machine can be operated either to charge an energy accumulator in the generator mode, or in the case of the boosting mode it can be supplied with energy from this energy accumulator.
According to this DE 103 59 071 B3, in a driving mode of the vehicle with a discharged energy accumulator, in which mode a boosting mode cannot be carried out, or can only be carried out to a restricted degree, a gear speed shift operation of a transmission is performed, for example shifting back by one or two gear speeds is performed, with the result that the internal combustion engine is as it were prestressed. At the same time, during this “prestressed” mode the energy accumulator is charged by the electric machine which is driven by the internal combustion engine. If an increased power demand is present, the internal combustion engine can more quickly make available the required power potential owing to the operation at an increased rotational speed; and at the same time the charging process is interrupted with the result that the internal combustion engine is additionally relieved of loading and in this way can additionally make available this power component to satisfy the increased power demand.